This proposal requests funds for a 13 element high energy resolution Ge array detector system to be used for x-ray absorption spectroscopy studies of dilute biological systems. Such studies, performed using synchrotron radiation, provide electronic and structural information about a selected absorbing atom with atomic numbers ranging from P through all of the transition metals. The Ge array detector, which is configured for ease of setup and use, will directly support the research of a group of 6 investigators, all of whom are interested in understanding aspects of the structure and function of various metal ions or metal-containing cluster sites in proteins. Specifically, Professor Hodgson and Dr. Hedman will study the MoFe protein and cofactor of nitrogenase and the iron site of methane monooxygenase. Professor Scott is involved in studies of Ni sites in several metalloproteins. Professor Penner-Hahn is interested in metalloprotein control of dioxygen metabolism by systems involving Mn, Fe, and Cu. The role of Cu in dioxygen binding and reactivity is being studied by Professor Solomon. Dr. Klein is investigating the role of Mn in the photosynthetic dioxygen evolving complex and of S in redox represents a quantitative increase in technological capacity that will enable many experiments on biological systems to be performed with much better S/N and will bring others into the realm of feasibility for the first time. The detector will primarily be used at the Stanford Synchrotron Radiation Laboratory where there is no similar instrumentation available.